The present invention pertains to the field of waste water treatment. In particular, the present invention provides a method for waste water treatment that is particularly effective in cold climates, such a those experienced in alpine areas or in Northern regions in winter.
Waste water is produced in large quantities throughout the year, by every community. By the term xe2x80x98waste waterxe2x80x99 is meant sanitary waste disposal water, i.e., the flow from sanitary sewers, industrial effluent, i.e., the flow from factories, mills, refineries, and other users of water in industrial settings, commercial effluent, i.e., the flow of waste water from service industries like restaurants and cleaning industries. In developed nations, it is desirable that 100% of waste water produced be treated in some way to ensure minimal negative environmental impact. To this end, most cities have built large sewage and waste water treatment facilities. These facilities are extremely expensive to build, operate and maintain, and they are of limited capacities.
If properly planned, waste water treatment facilities operate efficiently on a flow-through basis, and are able to process all of the waste water produced in any given period of time. However, efficient operation on such a basis is more difficult during winter months, when settling tanks may freeze, sewage lagoons freeze, rivers freeze over, but sewage keeps flowing in. Many facilities become over burdened by springtime flows, and it will be appreciated that by the time of the spring thaw, it has often been necessary to release untreated or partially treated waste water into the environment (i.e., receiving waters).
Furthermore, there are some communities located in Northern climes, or areas where sewage or waste water treatment is substantially impossible because the amount that must be stored over freezing months so far exceeds the amount that can practicably be processed during the milder months that a conventional treatment facility is not feasible. There are, similarly, communities such as ski and winter resort communities that have relatively small populations of permanent residents, but that support very large populations of winter visitors. These communities either do not have a summertime need for high capacity waste water treatment facilities, or must subject existing facilities to highly fluctuating seasonal loads.
There are also industrial processes carried out in Northern locations, for instance oil recovery from oil sands that use large quantities of water which is not easily processed with conventional technology. Food processing industries, moreover, are often in maximum production in the freezing months following a harvest, and therefore produce waste water during those months.
There are four basic principal concerns in dealing with normal sanitary waste water treatment. First, one must be concerned with the volume of waste water that is being treated. This is the concern that most affects cost: the object is to handle the largest volume of waste water by separation of the waste and nutrients from the water for the smallest expenditure.
Secondly, one is concerned with lowering the nitrogen content of the waste water to obtain treated water substantially free of nitrogen. Nitrogen, usually present as NH3, NH4+, NO3xe2x88x92, NO2xe2x88x92 and organic-N in waste water, is a potent pollutant because it provides an essential nutrient to many micro-organisms that may exist in water destined for human consumption.
Thirdly, it is essential to lower bacterial counts in treated waste water to below mandated levels, which levels are generally in the order of 100-1000 per 100 ml.
Lastly, for aesthetic water quality reasons, it is necessary to lower phosphorous levels in waste water. Phosphorous, generally present as soluble phosphate ions in waste water, should be preferably kept below about 1 mg/l and preferably below 0.05 mg/xe2x88x92_, to restrict algae and weed growth, since algae will deplete O2 in receiving waters.
The present invention, non-biological (psychromechanical) in basic concept, therefore, achieves each of the foregoing basic concerns, and provides a cost efficient method for treating large quantities of waste water from residential, commercial or industrial sources, in cold climates, to produce clean water without the need to store the waste water until milder weather prevails. The present invention has identified and advantageously utilizes a number of phenomena manifested during atomization and phase-change from liquid to solid of waste water under low temperature (sub-zero) atmospheric conditions. Moreover, the present invention does so in a process that differentiates it from previous attempts, all relatively unsuccessful, to efficiently utilize psychro-mechanical concepts in waste water treatment. For instance, in a study entitled xe2x80x9cLow-Temperature Sewage Disposal Through Snowmakingxe2x80x9d, by Zapf-Gilge, Russell and Mavinic, discussed the effects of concentrating impurities in the unfrozen portion of an ice pellet or similar structure. Zapf-Gilge et al, however, did not obtain viable results, finding unacceptably high concentrations of nitrogen and phosphorous in the resulting snowmelt water. Their study became, then, directed to suggestions on handling of the chronological melt fractions of a snowpack. The short coming of such a manner of approach is that it does not provide a method of treating waste water, it merely concentrates the impurities in the waste water, and results in a problem in the discharge water.
Moreover, in 1975, a method of xe2x80x9cStorage and Renovation of Sewage Effluent in Artificially Created Snowpackxe2x80x9d was proposed by Wright-McLaughlin Engineers of Denver, Colo., in a published report of December, 1975. This proposed method did not, however, recognize the need for 100% freeze out or phase change of the sewage water, which resulted in the manufacture of snow with up to about 38% liquid water content. As a result, the method was ineffective for treatment, as that term is used herein, and only marginally relevant for storage.
The present invention, however, provides a treatment method that does not merely concentrate nutrients and contaminants. The present invention essentially removes substantially all inorganic nitrogen from the waste water, while at the same time precipitating the phosphates therefrom as benign insoluble alkaline salts. Moreover, the method of the present invention results in virtually complete elimination of bacteria, cysts, spores and pathogens in the waste water.
In a broad aspect, therefore, the present invention relates to a method of processing waste water comprising atomizing said waste water under selected atmospheric conditions to achieve substantially complete phase change of said water to solid form.
In another broad aspect, the present invention relates to a method of conversion of soluble phosphate ions in waste water that includes phosphate ions, ammonia gas, ammonium ions, calcium ions and magnesium ions, comprising atomization of said waste water under atmospheric conditions appropriate for the substantially complete phase change of said waste water to ice crystals or water vapour, whereby ammonium ions under the influence of increased pH in said waste water form ammonia gas, and phosphate ions in said waste water combine with calcium or magnesium ions as calcium phosphate and magnesium phosphate respectively and precipitate as insoluble salts.